A multimedia device may be a piece of mobile communication equipment such as a mobile telephone, PDA, or the like having functionality over and above an FM radio. The multimedia device may however have no electronic functions other than those of a radio receiving apparatus.
The radio data system (RDS) is intended for application to VHF/FM sound broadcasts in the range 87.5 MHz to 108 MHz; these may carry either stereophonic or monophonic programs. The main objectives of RDS are to enable improved functionality of FM receivers and to make them more user-friendly by using features such as program service (PS) name, program type (PTY) and where applicable, automatic tuning for radios incorporated into mobile devices.
RDS is defined by the European Broadcasting Union (EBU)/Cenelec Standard EN50067: 1998, “Specification of the Radio Data System”. This standard is compatible with the United States radio broadcast data system defined by their National Radio Systems Committee in the specification of the radio broadcast data system, dated 9 Apr. 1998. In the following, it should be understood that the term RDS refers to both the Radio Data System and the Radio Data Broadcasting System.
FIG. 1 shows the structure of the baseband coding of the RDS standards. The largest element in the structure is called a group, consisting of 104 bits. Each group contains four blocks of 26 bits each. Each block contains an information word and a check word. Each information word comprises 16 bits, and each check word comprises 10 bits.
Each group contains message information; the message format and addressing structure are shown in FIG. 2. The first block in every group always contains a program identification (PI) code. The first four bits of the second block of every group are allocated to a 4-bit code that specifies how the information within the group is to be applied. Groups will be referred to as type 0 to 15 according to binary weighting A3=8, A2=4, A1=2, A0=1. For each type (0 to 15) two versions can be defined. The version is specified by a fifth bit (B0) of block 2.
a) B0=0: the PI code is inserted in block 1 only. This defines version A of the RDS encoding systems.
b) B0=1: the PI code is inserted in block 1 and block 3 of all group types. This defines version B of the RDS encoding systems.
Each block contains a Group Type Code (GTC) defining the nature of the information word of the block.
A mixture of version A and version B groups may be transmitted on one particular FM radio station. A program type code (PTY) and the traffic program identification (TP) occupy six locations in block 2 of every group.
The PI, PTY and TP codes can be decoded without reference to any block outside the ones that contain information relating to one of these codes. This is important to minimise acquisition time for these kinds of message and to retain the advantages of the short (26-bit) block length. To permit this to be done for the PI codes in block 3 of version B groups, a special offset word (commonly defined as C′) is used in block 3 of version B groups. The occurrence of offset C′ in block 3 of any group can then be used to indicate directly that block 3 is a PI code, without any reference to the value of B0 in block 2.
Table 1 gives the group type codes for both versions A and B of the RDS encoding system and a brief description of the data content of each group.
Table 2 gives repetition rates of some of the main features of RDS. A total of four type 0A groups are required to transmit an entire program service (PS) name, and therefore four type 0A groups are required per second according to the standard. The repetition rate of the type 0A group may be reduced if more capacity is needed for other applications. A minimum of two type 0A groups per second is necessary to ensure correct functioning of PS and alternative frequency (AF) features.
Circuits for receiving and decoding both audio and data components of an FM radio broadcast are known in the art. Indeed, an example of an FM receiver demodulator having an RDS demodulator and decoder is given in the radio broadcast data system standard.
Mobile devices, for example car stereos, incorporating FM radio receivers require frequent retuning due to spatial variation of intensity of FM radio signals. Further, the availability of radio stations varies between geographical regions. Normally, a user of a mobile radio will search a frequency band for a desired radio station, using a scan or seek function of the mobile radio. The mobile radio will scan for a signal and once locked on to a station, will receive and decode a PS code of the station in order to establish a respective program station name. The mobile radio may then display the program station name on an appropriate display means.
TABLE 1Group Type CodesGroup typeFlagged incode/versiontypeGroup typeA3A2A1A0B01A groupsDescription0A00000Basic tuning and switching information only (see 3.1.5.1)0B00001Basic tuning and switching information only (see 3.1.5.1)1A00010Program Item Number and slow labeling codes only (see 3.1.5.2)1B00011Program Item Number (see 3.1.5.2)2A00100RadioText only (see 3.1.5.3)2B00101RadioText only (see 3.1.5.3)3A00110Applications Identification for ODA only (see 3.1.5.5)3B00111Open Data Applications4A01000Clock-time and date only (see 3.1.5.6)4B01001Open Data Applications5A01010Transparent Data Channels (32 channels) or ODA (see 3.1.5.8)5B01011Transparent Data Channels (32 channels) or ODA (see 3.1.5.8)6A01100In House applications or ODA (see 3.1.5.9)6B01101In House applications or ODA (see 3.1.5.9)7A01110YRadio Paging or ODA (see 3.1.5.10 and annex M)7B01111Open Data Applications8A10000YTraffic Message Channel or ODA (see 3.1.5.12)8B10001Open Data Applications9A10010YEmergency Warning System or ODA (see 3.1.5.13)9B10011Open Data Applications10A 10100Program Type Name10B 10101Open Data Applications11A 10110Open Data Applications11B 10111Open Data Applications12A 11000Open Data Applications12B 11001Open Data Applications13A 11010YEnhanced Radio Paging or ODA (see annex M)13B 11011Open Data Applications14A 11100Enhanced Other Networks information only (see 3.1.5.19)14B 11101Enhanced Other Networks information only (see 3.1.5.19)15A 11110Defined in RBDS only15B 11111Fast switching information only (see 3.1.5.20)
TABLE 2Main feature repetition ratesGroup typesAppropriatewhich containrepetitionMain Featuresthis informationrate per sec.Program Identification (PI) codeall11.41Program Type (PTY) codeall11.41Traffic Program (TP) identification codeall11.41Program Service (PS) name4)0A, 0B1Alternative frequency (AF) code pairs0A4Traffic announcement (TA) code0A, 0B, 14B, 15B4Decoder identification (DI) code0A, 0B, 15B1Music/speech (M/S) code0A, 0B, 15B4Radiotext (RT) message2A, 2B0.22Enhanced other networks information14Aup to 23(EON)1Valid codes for this item will normally be transmitted with at least this repetition rate whenever the transmitter carries a normal broadcast program.2A total of 16 type 2A groups are required to transmit a 64 character radiotext message and therefore to transmit this message in 5 seconds, 3.2 type 2A groups will be required per second.3The maximum cycle time for the transmission of all data relating to all cross-referenced program services shall be less than 2 minutes.4PS must only be used for identifying the program service and it must not be used for other messages giving sequential information.
Due to the constraints of a typical mobile radio user interface, this is the only means available for searching an FM radio band. Further, due to the presence of alternative frequencies for a particular station, it is possible that the particular station may be encountered more than once during a search as described above.
An FM radio receiver with RDS may only perform a search on the whole frequency spectrum of the FM radio band. This is undesirable as a user travelling from their home region to another region may wish to listen to a particular radio station they heard while last visiting the another region, the particular radio station having a particular frequency. The user may not be able to remember the particular frequency of the particular radio station, but may be able to remember the entirety of or a portion of the radio station name.
With known FM radio receivers, the user will be forced to scan the whole frequency spectrum of the FM radio band manually in order to find the particular radio station that they wish to listen to.
It is an aim of embodiments of the present invention to solve or at least mitigate one or more of the problems described above.